Process of making styrenated phenolformaldehyde resins



2,859,265 or Mime STYRENATED PrrENoL- FORMALDEHYDE RESlNS FrankJosepHLec fiom West l"a., assignor to Monsanto Chemical Company, St.Louis, Mega-cor- .poration of Delaware PRGCESS No Dravving. Originalapplication August 6, 1354, Serial No. 448,370, new Patent No.2,793,105, dated May '21, 1957. Divided and this application Novembepz,1956, Serial No. 624,211 I I a 2 creams. Cl. 260-51) This inventionrelates to modified phenolic resins which may be employed as athermosettingbinder in "the manufacture of grinding wheelsfi Thisapplication is a-division "of my copending application S. N. 448,370,filed August 16', 1954, now U. S. 2,793,105.

Resin bonded grinding wheels are used quite extensively for manygrinding operations in which ceramic bonded wheels are of little value.The resin bonded wheels'generally comprise abrasive grits bonded with athermosetting resin such as phenolic, melamine, urea," etc., resins.fOne objection to these materials-as bonding mediumfor the abrasivegrits is the brittleness of "the bond which causes a relatively rapiddeterioration'of the grinding wheel made therewith. 7 V 1 Effortshavebe'en made to decrease the brittleness of the thermosetting bondbymixing a thermoplastic resin with the thermos'etting resin while thelatter isstill'in .eration, segregation of polyvinyl 'butyral in "theresin matrix, and because of loss in flexural strength'of the grindingwheels due to the addition'of the thermoplastic resin; e

One object of this invention is to provide grinding wheels made Withaphenolic-polyvinyl acetal resin bond and having improved tlexuralstrength and greateruniformity in the cured piece (i. e. no softspots);;

A further object is to modify phenolic-polyvinyl butyr al resin"bonding-media to improve the-flow thereof in the molding operation; j

.7 These and other objects are attained by reacting monomeric styrenewith a phenol under acid conditions; immediately thereafter reacting theproduct with'formaldehyde to form a fusible resin and' then admixing theproduct with a polyvinyl acetal resin and forming 'grinding wheels fromthe mixture.

The following examples are given in illustration and are not intended aslimitations on-the scope .of this in vention. Where parts are mentionedthey are parts by weight. a J

EXAMPLE I Mix together 100 parts of phenol, 15 parts of styrene, 4 partsof oxalic acid and'1.5' parts of b'oricacid. Heat the mixture underreflux at 160-175 C. with constant agitation for about 1.5 hours. Thenadd 68 parts of formalin (37% formaldehyde). over a period of about 115hours while maintainingrefluxing conditions. The temperature during thisstep will fall to about 100 3C. due to the presence of the Water in-theformalin. Continue refluxing the reaction medium after the finaladdition of formalin until the reaction medium contains 0.5% or less offree formaldehyde. Then dehydrate the reaction medium under vacuum toobtain a solid brittle resin. For

- '2 purposes of further description this'will be called resin A.Resin'A is a fusible thermoplastic material since' it is prepared with adeficiency 'of formaldehyd'ej i'.e.j," less than 1 mol of formaldehydeper l-rirolofphehohfflo make it thermosettin'g, it'sliould'be blendedwith}! hardening agent such ashexarriethyleiie-tetraminegparaforinaldehyde, etc. This blendingis'generally*donein"the dry condition. 1 Y To form the grinding wheels ofthis invention, resin A is blended in the dry pulve'rule'nt formwith-thejhaid' hing agent and apolyvinyl acetal resin. This blend" 1sthen further modified by the incorporation increment-sire such ascryolite', abrasi've'griains 'suclr'aluminn grits, and a liquid materialsuch as a',liqur'd"p resin, furfural, etciwhich acts as alubricarr agentfor the abrasive grains. The blended I then pressed in a'p'rop'errrmldat 1000p. i.'an L for three days at temperatures'ris'ing slowly-from'temperatureto175"C.

' A representative formula for the grinding. whee blend is as follows:71

Parts Resin A I V Polyvinyl butyral resin I15 Hexamethylene tetramine 10'Wetting agent 45 Filler. {7'0 Abrasive grains 1400 Grinding wheels'prepared from the formula shown above are exceptionally uniform. andwhen broken apart it was observed'that the resin had flowed completelyand evenly during the curing operation. 1

In order to check'the flow properties of resin A alone and admixed withthe polyvinyl acetal'resin and to compare resin A with a similar resinmade from phenoland formaldehyde without the styrene, melting point andoven flow tests may be used i a For comparison, prepare a resin bymixing together parts of phenol, 72 parts of formalin and 2 parts ofoxalic acid. Heatthe mixture'at reflux temperature until less than 0.5%-free formaldehyde can --be detected and then dehydratethe reactionmedium undervacuum to obtain a dry brittle resin. Pulverize theresin.Thisresin tip the surface to an-angle 65 from the horizontal-andcontinue heating the surface and-pill at 1255C. -for-17 minutes. Theamount that the resin flows is measured inmillimeters. ,The results oftests on resins A and B blended with 10 parts of hexamethylene per 100parts of resin and with and without 15 parts of polyvinyl butyralresin-are shown in Table I. v V a Table I Polyvinyl Melting Oven ResluButyral Point, .Flow,

107 None The figures in" TableI Show that the additionoftlrjepoly vinylbutyral resin increases the melting point of both resin A and resin Band decreases the oven flow of A to 16 mm. and of resin 13 to such anextent that no flow 2,859,205. Patented Nov. 4, 1958 i occurs. Thus thecombination of resin A and the polygrinding wheels.

It would be expected that the lower melting point of resin A and itsgreater flow properties would result in grinding wheels having decreasedflexural strength. Since it is difficult to measure accurately theflexural strength of materials in the form of a wheel, prepare bars 6" x1" x 1" from the formulations shown in Table I and test them by thegeneral method described in ASTM D790-49T using a 4 inch span and across-head speed of 0.05 inch/min. It will be found that the meanflexural strength of resin A and resin B, each modified with parts ofhexamethylene tetramine is about the same, i. e., 4,137 p. s. i. and4,341 p. s. i. respectively. However when these resins are each modifiedwith parts of polyvinyl'butyral resin, it is found that the meanflexural strength of the formulation containing resin A' is about 3,744p. s. i. whereas the mean flexural strength of the formulationcontaining resin B is 2,961 p. s. i. This difference represents morethan a loss in flexural strength if resins of the type of resin B areused.

The resins of this invention are prepared by reacting styrene with amonohydricphenol under acid conditions and immediately after completionof saidreaction con densing the product with less than one mol offormaldehyde for each mol of phenol Thecondensation reaction iscontinued until substantially all of the formaldehyde is chemicallycombined. The resin thus produced is recovered and dry blended withahardener and a polyvinyl acetal resin.

Theamount of styrene may vary from 0.1 to 0.2 mol per mol of phenol. Thestyrene may be replaced in whole or in part by ring-substituted styrenesuch as monoand polychlorostyrene, mono-and polyalkyl .styrenesespecially the methyl styrenes,

As a matter of convenience in describing the invention, the resins andthe formulations are based on 1 mol of phenol. The phenolmay besubstituted in whole or in part by cresols or xylenols.

The catalyst'for the reaction between the styrene and the phenol and thesubsequent reaction with formaldehyde should be an acid or mixture ofacids. Preferably a mixture of oxalic acid and boric acid is used in anamount varying between 4 and 8 parts of total acid per 100 parts ofphenolic component. Other acids such as sulfuric, hydrochloric, formic,acetic, etc. acids may be used.

The reaction between the styrene and phenolic components is carried outat temperatures from 150 200 C. and the reaction is continued tocompletion. For styrene and phenol this generally takes from 1 to 2hours.

Immediately after completion of the reaction between the styrene andphenolic components from 0.7 to 0.9 mol of formaldehyde in the form ofan aqueous solution should be added to the hot reaction medium. Theaddition of the formaldehyde should take place over a period of from 1-4hours. Since the reaction is maintained under reflux conditions, thewater in the formaldehyde solution causes an immediate reduction intemperature to 'about 100 C. After all'the formaldehyde has been added,the reaction under reflux conditions should be continued untilsubstantially all of the formaldehyde has beenchemically combined. Atthis point the desired resin has been formed and is recovered from thereaction medium by dehydration, preferably under vacuum. The product isa solid brittle resin that can be easilypulyerized. The resin ispermanently thermoplastic. To render it thermosetting,.it .musthe mixedor blended with a hardening agent such as hexam'ethylen'e tetrainine, orthe solid polymers of formaldehyde such as paraform. From. 6 to 12 partsof hardening agent are necessary for each 1' parts of resin.

To formulate the grinding wheel binders of this invention, 100 parts ofthe pulverized resin are mixed with from 10 to 20 parts of a polyvinylacetal resin and the requisite amount of hardening agent. The pulverizedresin should be blended in the dry state with the solid hardening agentand the polyvinyl acetal resin in pulverw ulent form. The most usefulpolyvinyl. acetal resin is the polyvinyl butyral resin made by reactingbutyraldehyde with a hydrolyzed polyvinyl ester containing from a 05%residual ester groups. The resin will contain from 15-25% residualhydroxyl groups and the balance will be butyraldehyde acetal groups.Polyvinyl acetals made from formaldehyde, acetaldehyde andpropionaldehyde or mixtures thereof may be used to replace the polyvinylbutyral in whole or in part. 7

To form the grinding wheels, the resin blend .is' fur-. ther mixedwithabrasive grains and a filler; From 5 to 15 parts of resin blend areused for each 100 parts.0f abrasive grains and from 40 to 60 parts offiller are used. for each 100 parts of resin blend. The abrasive grains.may be any of the well-known hard inorganic materials such as aluminumoxide grit, sand, silicon carbide,-etc. The filler should be a mineralsomewhat softer than the I abrasive grits, such as cryolite.

After thorough blending of the grains, iilleriand resin 0 mixture, thegrinding wheel is formed by molding under.

uniform distribution of the dry resin bond and to yield.

a more uniform product. Liquid phenolic resins, .furfural, and otherliquid materials may be used for. this purpose.

What is claimed is: a V

1. A process for preparing a permanently fusible resin which comprisesreacting one mol of a monohydric phenol taken from the group consistingof phenol, cresols, xylenols and mixtures thereof with 0.1-0.2 mol of astyrene taken from the group consisting of styrene, ring-substitutedchlorostyrenes, ring-substituted alkylstyrenes, and mixtures thereof atreflux temperature underacid condi-. tions and immediately after thereaction is completed. adding 0.7-0.9 mol of an aqueous solutionof'formaldehyde to the reaction medium under reflux conditions and thencontinuing the reaction until substantially all the formaldehyde ischemically combined.

2. A process for preparing a permanently fusible resin: which comprisesreacting one mol of phenol with 0.1-0.2 mol of styrene at refluxtemperatures under acid condi: tions and immediately after the reaction'is completed adding 0.7-0.9 mol of an aqueous solution of formal--dehyde to .the reaction medium under reflux conditions and thencontinuing the reaction until substantially all 1 the formaldehyde ischemically combined.

References Cited the file of this patent l V UNITED STATES PATENTS. 7

'Teot July 1,

1. A PROCESS FOR PREPARING A PERMANENTLY FUSIBLE RESIN WHICH COMPRISESREACTING ONE MOL OF A MONONYDRIC PHENOL TAKEN FROM THE GROUP CONSISTINGOF PHENOL, CRESOLS, XYLENOLS AND MIXTURES THEREOF WITH 0.1-0.2 MOL OF ASTYRENE TAKEN FROM THE GROUP CONSISTING OF STYRENE, RING-SUBSTITUTEDCHLOROSTYRENES, RING-SUBSTITUTED ALKYSTYRENES, AND MIXTURES THEREOF ATREFLUX TEMPERATURE UNDER ACID CONDITIONS AND IMMEDIATELY AFTER THEREACTION IS COMPLETED ADDING 0.7-0.9 MOL OF AN AQUEOUS SOLUTION OFFORMALDEHYDE TO THE REACTION MEDIUM UNDER REFLUX CONDITIONS AND THENCONTINUING THE REACTION UNTIL SUBSTANTIALLY ALL THE FORMALDEHYDE ISCHEMICALLY COMBINED.